29 June 2000 STEPS Supercell Storm: Relationships Between Kinematics, Microphysics, and Lightning

We investigate the kinematic, microphysical and electrical evolution of a tornadic supercell storm which occurred on June 29, 2000 during the Severe Thunderstorm Electrification and Precipitation Study (STEPS). This storm was well-sampled by at least two Doppler radars and one multi-parameter radar from 21:30 through 01:20 UTC. In addition, the location and intensity of the lightning activity in this storm was measured by the National Lightning Detection Network (NLDN) and the New Mexico Tech Lightning Mapping Array (LMA). Flash rates in this storm exceeded 300 flashes per minute. The storm produced only intracloud flashes for the first two hours. When the storm did finally produce cloud-to-ground (CG) flashes, they were almost all positive (+CGs). In general, we find very good correlations between total flash rate, volume of updraft, and volume of graupel. Specifically, each surge in flash rate was preceded by (or coincident with) surges in volume of updraft exceeding 10 ms^-1 and in volume of graupel. The largest of these surges was nearly coincident with the right turn of the storm, tornado touchdown, a sharp increase in hail, and initiation of frequent +CG flashes. The NLDN and LMA data indicate that these +CG flashes usually clustered near the precipitation core of the storm and that the +CGs originated from a positive charge region at mid-levels (6-8 km MSL), not the anvil. Both hail and graupel were highly concentrated in this inferred +CG source charge region; however, +CGs did not occur unless there was hail.